Lesson Notes By Weeks and Term v4 - SHS 3
ALTERNATING CURRENT
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ALTERNATING CURRENT
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Subject: Physics
Class: SHS 3
Term: 2nd Term
Week: 7
Grade code: 3.3.1.LI.2
Strand code: 3
Sub-strand code: 2
Content standard code: 3.3.2.CS.1
Indicator code: 3.3.1.LI.2
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: ALTERNATING CURRENT
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This lesson introduces Alternating Current (AC), the type of electricity supplied to our homes and schools by the Electricity Company of Ghana (ECG). Unlike Direct Current (DC) from batteries which flows in one direction, AC constantly changes direction. Understanding AC is crucial because it powers almost everything around us, from the lights in our classrooms and the fans that cool us down, to the refrigerators in our kitchens and the televisions in our living rooms. We will explore the characteristics of AC, including its different shapes (waveforms) and the important concepts of peak and RMS values, which are essential for understanding electrical safety and how our appliances work.
2.1 What is Alternating Current (AC)?
Alternating Current (AC) is a type of electrical current in which the flow of electric charge periodically reverses direction. In contrast, Direct Current (DC), which we get from batteries, flows in only one direction. Analogy: Think of DC as water flowing steadily in one direction down a river. AC is like the tide at the beach, where the water flows in and then flows back out, constantly changing direction.
The electricity supplied by ECG to our homes in Ghana is AC. It has a frequency of 50 Hertz (Hz), which means it changes its direction and comes back to the start 50 times every second. 2.2 Types of AC Waveforms
An AC waveform is a graph that shows how the voltage or current changes over time. While there are many types, we will focus on three common ones. Sinusoidal Waveform: Description: This is a smooth, repetitive, wave-like curve. The voltage or current increases to a maximum positive value, decreases through zero to a maximum negative value, and then returns to zero. Importance: This is the most efficient and common type of AC waveform. It is the type generated by ECG and used in our homes. Appearance: Square Waveform: Description: This waveform instantly switches between a fixed maximum positive value and a fixed maximum negative value. It spends no time in between these levels. Importance: It is commonly used in digital electronics and computer circuits to represent binary states (1s and 0s). Appearance: Triangular Waveform: Description: This waveform increases and decreases at a constant (linear) rate, creating a shape like a series of triangles. A special case is the sawtooth wave, which rises slowly and drops instantly, or vice versa. Importance: It is used in sound synthesisers and for scanning the display in older CRT televisions. Appearance: 2.3 Key AC Terminology and Calculations